1. Field of the Invention
The present invention relates to a method and an apparatus for obtaining irradiation intensity of a laser beam, and an apparatus for irradiating the laser beam.
2. Description of Related Art
Conventionally, an apparatus which irradiates a laser beam is used in a variety of fields for medical treatment and processing. For example, in the field of ophthalmology, there is known a laser irradiation apparatus which changes a corneal curvature by ablating a cornea with irradiation of an excimer laser beam, and to correct a refractive error of an eye. In this kind of apparatus, irradiation intensity distribution in an irradiation area of the laser beam (a cross-sectional area of the laser beam to be irradiated) and/or in an ablation area varies because of time-course change of an irradiation optical system or the like, and consequently, an ablation shape such as ablation depth distribution sometimes varies. Therefore, it is necessary to adjust the laser irradiation according to those variations.
In order to adjust the laser irradiation, the applicant has proposed, in Japanese Patent Application Unexamined Publication No. Hei6-226471 corresponding to U.S. Pat. No. 5,624,436, a method for forming a curved surface on a transparent plate (PMMA plate) having a known ablation rate by laser irradiation so as to have predetermined refractive power, then measuring the refractive power of the curved surface with a lens meter, and calibrating data for ablation based on the measurement result.
According to the above method, it has become possible to easily adjust the laser irradiation in correspondence with the variations in the irradiation intensity distribution and the ablation shape; however, a further technique for attaining more accurate ablation is desired.